Collaborative Research: Using Multisystem Deep-Time Thermochronology to Decipher Neoproterozoic Exhumation Patterns in Time and Space

合作研究：利用多系统深时热年代学破译新元古代的时空折返模式

• 批准号: 2044603
• 负责人: Peter Zeitler
• 金额: $ 11.08万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-15 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2044603&HistoricalAwards=false
• 关键词: Collaborative; Research; Using; Multisystem; Deep

Earth’s history as recorded in rocks is frequently incomplete in any one place, with gaps of missing time known as unconformities. While common, such gaps typically occur at different times in different places. A major exception is the unusual abundance of such gaps across multiple continents shortly before the start of the current geological Eon, and shortly before the diversification of shelly fossils in the famous Cambrian Explosion. The origin of this global gap in the rock record, known as the Great Unconformity, has been a subject of debate for some time. One of the recently proposed hypotheses links the unconformity to glacial erosion during the global “snowball Earth” ice ages that occurred about 715-660 and 740-735 million years ago. Because erosion decreases the depth (and thus temperature) of rocks beneath the surface of the crust, one test of this hypothesis involves minerals known as thermochronometers. These minerals record the past temperatures that they have experienced over time, due to (for instance) the rate of diffusion of isotopes produced in these minerals at a known rate by radioactive decay. While time alone provides some constraints on the cause of erosion, the time resolution of thermochronometers is limited in rocks this old. Consequently, in order to distinguish glacial erosion from erosion associated with the normal operation of plate tectonics, we propose to study not only the timing but also the spatial pattern of erosion over this time period, using thermochronometers collected from both stable continental interiors and less stable continental margins. Since the glacial erosion hypothesis predicts substantial erosion of stable crust in the interior of the continents, while the tectonic hypothesis predicts erosion only near tectonically active regions, the spatial distribution of erosion will allow us to determine whether erosion associated with the Great Unconformity was the result of glacial processes, tectonic processes, or both. The results will allow us to formulate and test new questions about the environmental consequences of the Great Unconformity, and the relationship between the Great Unconformity and the Cambrian Explosion. In addition to producing peer-reviewed publications and open-source software, our results will be incorporated into professional video content designed to be accessible to the broader public and for use in undergraduate courses. The Neoproterozoic Era encompassed a number of significant changes in Earth’s systems, including major diversification and complexification of the biosphere, episodes of extreme glaciation, and breakup of the supercontinent Rodinia. Preliminary data suggest that this time interval also saw a period of surprisingly robust erosional exhumation on the order of several km. Such exhumation could be a key link in connecting Earth-system processes, if it were widespread enough in extent, significant enough in magnitude, and had the correct timing. Recently, Keller et al. (2019) proposed a link between widespread glaciation and cratonic exhumation, specifically linking Neoproterozoic “Snowball Earth” glaciations to the phenomenon of widespread unconformity spanning the late Neoproterozoic. However, this proposal has subsequently been contested by Flowers et al. (2020), who instead attribute late Neoproterozoic exhumation and the Great Unconformity to normal tectonic processes associated with the breakup of Rodinia, and propose that Neoproterozoic glaciation had little if any erosive impact. Unfortunately, many previous thermochronologic studies, including that of Flowers et al., have focused on regions that were cut by Neoproterozoic faults, not truly tectonically stable — requiring the two hypotheses to be differentiated by timing alone, a tricky proposition given the large time uncertainty of thermochronologic time-temperature (t-T) inversions. Here we will propose a new thermochronologic test, based instead on the contrasting spatial patterns of exhumation predicted by tectonic and glacial mechanisms between stable cratonic interiors and less stable, tectonically active regions. This project will provide integrated research experience and professional-development training for a first-generation- postdoctoral fellow, who will collaborate across three institutions (Lehigh, Dartmouth, and Illinois), and will support two early-career PIs. Undergraduates at all three collaborating institutions will also be engaged in the project as summer interns and receive exposure to the research process, including experimental planning and communication of results. Given the level of public interest in the Great Unconformity, we will collaborate with Kindea Labs to produce content that can be integrated both in undergraduate class lessons and in popular science media.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

岩石中记录的地球历史在任何地方经常是不完整的，缺少时间的差距被称为不整合。虽然常见，但这种差距通常在不同地方的不同时间发生。一个主要的例外是，在当前地质EON开始之前不久，在著名的寒武纪爆炸中的雪莉化石多样化之前，多个大洲的这种差距异常。一段时间以来，岩石记录中这个全球差距的起源一直是辩论的主题。最近提出的假设之一将不整合性与全球“雪地地球”冰河时代的冰川侵蚀联系起来，大约715-660和740-7.35亿年前。由于侵蚀减少了地壳表面以下岩石的深度（以及温度），因此该假设的一种检验涉及称为热化学计的矿物质。这些矿物质记录了它们随着时间的流逝的过去温度，因为（例如）以放射性衰减的已知速率在这些矿物质中产生的同位素扩散率。虽然单独的时间对侵蚀的原因提供了一些限制，但热力学计的时间分辨率在此旧的岩石中受到限制。因此，为了区分冰川侵蚀与与板块构造的正常运行相关的侵蚀，我们建议使用从稳定的连续内部内部和较不稳定的连续边缘收集的热化学计收集的热对照器，不仅研究时间安排，而且还研究了这段时间内侵蚀的空间模式。由于冰川侵蚀假说预测了大陆内部稳定地壳的实质性侵蚀，而构造假说仅预测侵蚀附近涉及构造活性区域，因此侵蚀的空间分布使我们能够确定与伟大的不成熟性相​​关的侵蚀是导致熟悉过程的结果。结果将使我们能够提出和测试有关巨大不整合的环境后果以及巨大不整合与坎布里亚爆炸之间的关系的新问题。除了生产经过同行评审的出版物和开源软件外，我们的结果还将纳入专业的视频内容中，旨在可供广泛的公众访问并供本科课程使用。新元古代时代涵盖了地球系统的许多重大变化，包括生物圈的重大多样化和络合，极端冰川的发作以及超大陆罗迪尼亚的破裂。初步数据表明，此时间间隔还看到了一段令人惊讶的稳健侵蚀性挖掘，几个公里的顺序。这样的挖掘可能是连接地球系统过程的关键链接，如果它的宽度足够宽度，幅度足够重要，并且具有正确的时机。最近，Keller等人。 （2019年）提出了广泛的冰川和克拉通挖掘之间的联系，特别是将新元古代的“雪地地球”冰川与跨越晚期Neoperorogoic的广泛不整合现象联系起来。但是，该提议随后受到Flowers等人的争议。 （2020），他相反，将晚期的新元古代挖掘和与Rodinia破裂相关的正常构造过程的极大不整合归因于晚期，并且提议Neoperoroderocic Glaciation几乎没有任何侵蚀性影响。不幸的是，许多先前的热量研究（包括Flowers等人的热量研究）都集中在因新元古代断层所切割的区域上，而不是真正构造稳定的区域 - 要求单独使用这两个假设来区分这两个假设，这是一个棘手的提议，这是一个棘手的命题，鉴于热力学时间 - 素养时间 - 过程（T-T-T-T-T-T-T-T-T-T-T-T-T-T）的构图。在这里，我们将提出一项新的热量测试，取决于稳定的克拉托式内饰和较不稳定的，构造的活性区域之间的构造和冰川机制所预测的对比的空间模式。该项目将为第一代博士后研究员提供综合的研究经验和专业发展培训，该研究员将在三个机构（Lehigh，Dartmouth和Illinois）之间进行合作，并将支持两个早期职业PIS。所有三个合作机构的本科生也将作为暑期实习生从事该项目，并接受研究过程，包括实验计划和结果。鉴于对大不整合的公众兴趣水平，我们将与Kindea Labs合作生产可以在本科课程课程和流行科学媒体中整合的内容。该奖项反映了NSF的法定任务，并被认为是通过基金会的知识分子优点和更广泛影响的审查标准来通过评估来获得的支持。